1. Field of the Invention
The present invention concerns an improved fastener for connecting two walls defining an enclosure for a two-spool tape cartridge in which a flexible, elastic drive belt contacts the tape on the tape spools and whereby movement of the belt causes movement of the tape between the spools.
2. Description of the Prior Art
The belt driven cartridge of U.S. Pat. No. 3,692,255, issued to Von Behren and assigned to the assignee of the present invention, has been very successfully utilized to interface with computers where rapid acceleration and deceleration of the tape are required. In the cartridge there disclosed, a magnetic recording tape is convolutely wound on two tape spools and is bidirectionally driven between the spools by an endless flexible belt in frictional contact with the tape on both spools. The cartridge itself includes a thin base plate, usually of aluminum, and a clear or translucent polymeric cover which is conventionally attached to the plate with screws to define a thin, generally rectangular enclosure.
When the cartridge of the Von Behren patent was first marketed in 1972, its magnetic recording tape had a width of 1/4 inch (6.35 mm), a thickness of 1 mil (0.025 mm), and was driven at 30 inches (762 mm) per second. Data were originally recorded on the tape at a density of 1600 flux reversals per inch (63 per mm). Current cartridges come in a variety of sizes and the recording tapes range in width from 0.150 inches (3.81 mm) to 0.250 inches (6.35 mm), may be as thin as 0.6 mil (0.015 mm), may be driven at 90 or more inches (2286 mm) per second, and data is recorded at densities of 10,000 flux reversals per inch (394 per mm) or more. In addition, data are recorded on a plurality of independent, parallel tracks, which may number in excess of 32, spaced across the width of the magnetic recording tape.
It has been discovered that the differential thermal coefficients of expansion and the inflexible screw fastening between the polymeric cover and the aluminum plate causes the cartridge to bow to a maximum deflection at its center of approximately 0.005 inches (0.125 mm) over the temperature range which may be encountered during operation. Although this deflection did not cause a problem when the cartridge was first introduced, the higher tape speeds, recording densities, and track densities have created a need for a more stable cartridge which remains flat when exposed to temperature extremes.